Amoxicillin and potassium clavulanate are respectively a known β-lactam antibiotic and a known β-lactamase inhibitor. Products comprising amoxicillin and potassium clavulanate are marketed under the trade name “Augmentin” by SmithKline Beecham. Such products are particularly effective for treatment of community acquired infections, in particular upper respiratory tract infections in adults and otitis media in children.
Various tablet formulations of amoxicillin and potassium clavulanate have been approved for marketing, comprising various different weights and ratios of amoxicillin and potassium clavulanate, for instance, conventional swallow tablets comprising 250/125, 500/125, 500/62.5, and 875/125 mg amoxicillin/clavulanic acid (in the form of potassium clavulanate). Such tablets comprise amoxicillin and clavulanic acid in the ratio 2:1, 4:1, 8:1 and 7:1, respectively. The 875/125 mg tablet was developed to provide a tablet formulation which could be administered in a bid (twice daily) dosage regimen It is also marketed for tid (three times daily) dosing, in Italy and Spain. The 500/62.5 mg tablet was also developed to provide a tablet formulation which could be administered in a bid dosage regimen, two such tablets being taken every 12 h, in preference to a single 1000/125 mg tablet. A 1000/125 mg single dosage is also available, in France, but as a single dosage sachet rather than a tablet. Typically, the approved regimens provides a single dosage of 125 mg of potassium clavulanate.
In addition, WO 97/09042 (SmithKline Beecham) describes tablet formulations comprising amoxicillin and clavulanic acid in a ratio in the range 12:1 to 20:1, preferably 14:1. Furthermore, it is suggested that the preferred dosage of 1750/125 mg may be provided as two tablets, the first comprising 875/125 mg amoxicillin and clavulanic acid and the second 875 mg amoxicillin. The 14:1 ratio is said to be useful for the empiric treatment of bacterial infection potentially caused by drug resistant S pneumoniae (DRSP). This patent application also describes paediatric formulations comprising amoxicillin and clavulanate in a 14:1 ratio, for administering amoxicillin dosages of 90 mg/kg/day. Data suggest that such a dosage may provide antibiotic concentrations sufficient to eradicate DRSP with amoxicillin +/−clavulanic acid MICs≦4 μg/ml (Bottenfield et al, Pediatr Infect Dis J, 1998, 17, 963-8).
WO 94/16696 (SmithKline Beecham) discloses generally that clavulanic acid may unexpectedly enhance the efficacy of amoxicillin against microorganisms having a resistant mechanism which is not β-lactamase mediated.
Existing marketed tablet formulations of amoxicillin and potassium clavulanate are conventional in that they provide immediate release of the active ingredients once the tablet reaches the stomach. There has also been some interest in developing formulations in which the release profile is modified, to allow for a longer interval between dosages, for instances, every 12 hours (bid, q12 h), rather than every 8 hours (tid, q8 h).
Thus, for instance, WO 95/20946 (SmithKline Beecham) describes layered tablets comprising amoxicillin and, optionally, potassium clavulanate, having a first layer which is an immediate release layer and a second layer which is a slow release layer. The broadest ratio of amoxicillin to clavulanic acid is 30:1 to 1:1, with a preferred range of 8:1 to 1:1. Amoxicillin is suitably in the form of amoxicillin trihydrate. Examples provided of such bilayered tablets have amoxicillin trihydrate in the immediate release layer and amoxicillin plus clavulanate in the slow release layer. Multi-layered tablets are described more generically in WO 94/06416 (Jagotec A G). Further bilayered tablets comprising clavulanic acid and amoxicillin are described in WO 98/05305 (Quadrant Holdings Ltd). In such tablets, a first layer comprises amoxicillin and a second layer comprises clavulanate and the excipient trehalose, to stabilise the clavulanate component.
In addition, WO 95/28148 (SmithKline Beecham) describes amoxicillin/potassium clavulanate tablet formulations having a core containing amoxicillin and potassium clavulanate coated with a release retarding agent and surrounded by an outer casing layer of amoxicillin and potassium clavulanate. The release retarding agent is an enteric coating, so that there is an immediate release of the contents of the outer core, followed by a second phase from the core which is delayed until the core reaches the intestine. Furthermore, WO 96/04908 (SmithKline Beecham) describes amoxicillin/potassium clavulanate tablet formulations which comprise amoxicillin and potassium clavulanate in a matrix, for immediate release, and granules in a delayed release form comprising amoxicillin and potassium clavulanate. Such granules are coated with an enteric coating, so release is delayed until the granules reach the intestine. WO 96/04908 (SmithKline Beecham) describes amoxicillin/potassium clavulanate delayed or sustained release formulations formed from granules which have a core comprising amoxicillin and potassium clavulanate, surrounded by a layer comprising amoxicillin. WO 94/27557 (SmithKline Beecham) describes controlled release formulations of amoxicillin and clavulanic acid prepared using a hydrophobic waxy material which is then subjected to thermal infusion.
Controlled release formulations comprising amoxicillin have been described by several groups. Thus, Arancibia et al ((Int J of Clin Pharm, Ther and Tox, 1987, 25, 97-100) describe the pharmacokinetic properties and bioavailability of a controlled release formulation comprising 500 mg of amoxicillin. No further details of the formulation are provided. The formulation was however designed to release 21 to 35% during the first 60 minutes, 51 to 66% at 4 hours, 70 to 80% at 6 hours, 81 to 90% at 8 hours and more than 94% at 12 hours. They however found little, if any, correlation between the in vitro dissolution rate and the pharmacokinetic behaviour in the body. Hilton et al (International Journal of Pharmaceutics, 1992, 86, 79-88) described an alternative controlled release tablet having a hydrophilic polymer matrix and a gas release system, to provide intragastric buoyancy, to enhance gastric retention time. This showed no advantage over a conventional capsule formulation, with bioavailability being diminished. In contrast, Hilton et al (Journal of Pharmaceutical Sciences, 1993, 82, 737-743) described a 750 mg controlled release tablet incorporating the enteric polymer hydroxypropylmethyl cellulose acetate succinate. This however failed to show any advantage over a conventional capsule. In particular, the bioavailability was reduced to 64.6% compared with the same dosage provided in a capsule. More recently, Hoffman et al (Journal of Controlled Release, 1998, 54, 29-37 and WO 98/22091) have described a tablet comprising 500 mg of amoxicillin in a matrix comprising hydroxypropyl methyl cellulose, designed to release 50% of its contents in the first three hours and complete the drug release process over eight hours. The time above MIC was found to be significantly extended, compared to a capsule formulation, but not enough for a 12 h dosing interval. The discussion is in the context of a theoretical MIC of 0.2 μg/ml.
It has therefore, been determined that there is a continuing need to provide new dosage regimens for amoxicillin/clavulanate which are effective against more resistant bacteria.